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      <title>Thymeleaf - 交互式测验</title>
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    </head>
    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>Thymeleaf - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
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                    <div id="question-container">
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                  <button id="prev-btn" class="nav-btn">上一题</button>
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                  <button id="next-btn" class="nav-btn">下一题</button>
                </div>
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      </div>

      <script>
        const quizData = [
  {
    "question": "根据CAP理论，在分布式系统中，当网络分区（P）发生时，系统设计者必须在哪个两个特性之间做出权衡？",
    "options": [
      "可用性（A）和持久性（D）",
      "一致性（C）和可用性（A）",
      "一致性（C）和原子性（A）",
      "分区容错性（P）和一致性（C）"
    ],
    "correctAnswerIndex": 1,
    "explanation": "CAP理论的核心在于，任何分布式系统最多只能同时满足一致性（Consistency）、可用性（Availability）和分区容错性（Partition tolerance）中的两项。由于网络分区在分布式环境中是不可避免的，因此P是必须保证的前提。这就迫使我们在系统设计时，必须在数据强一致性（C）和系统高可用性（A）之间做出选择。",
    "source": "文档中「CAP 定律与 BASE 理论」部分",
    "hint": "文档中提到：“当网络分区发生时，你必须做出一个选择：是选择返回可能过时的数据（保证A），还是选择报错或无限等待（保证C）。”"
  },
  {
    "question": "两阶段提交（2PC）协议存在一个主要缺陷，即它是一种同步阻塞协议。在什么情况下，这种缺陷会导致所有参与者资源被长期锁定？",
    "options": [
      "协调者在第一阶段（准备阶段）发送“prepare”请求后崩溃",
      "某个参与者在第一阶段（准备阶段）投票“abort”",
      "协调者在第二阶段（提交阶段）成功发送“commit”请求后崩溃",
      "协调者在第二阶段（提交阶段）发送“commit”请求前崩溃"
    ],
    "correctAnswerIndex": 3,
    "explanation": "2PC最大的问题在于同步阻塞。如果协调者在完成第一阶段的“prepare”并收集到所有参与者的“yes”响应后，但在向大家发送“commit”指令之前崩溃，那么所有已经锁定资源的参与者都会陷入无限等待的状态。它们不知道最终的决定是提交还是回滚，只能一直阻塞，直到协调者恢复。",
    "source": "文档中「两阶段提交 (2PC)」的「缺点」部分",
    "hint": "思考一下，在2PC流程中，哪个时间点的协调者宕机会让参与者陷入“既不知道该提交，也不知道该回滚”的 limbo 状态。"
  },
  {
    "question": "与2PC相比，三阶段提交（3PC）协议引入了哪个关键阶段来减轻阻塞问题？",
    "options": [
      "Pre-Commit (预提交阶段)",
      "Pre-Vote (预投票阶段)",
      "Post-Commit (后提交阶段)",
      "Validation (验证阶段)"
    ],
    "correctAnswerIndex": 0,
    "explanation": "3PC通过在2PC的“准备阶段”和“提交阶段”之间增加一个“CanCommit/Pre-Commit”（预提交）阶段来改进。这个阶段用于在锁定资源前进行一次确认，并引入了超时机制。如果在预提交阶段后，参与者没有及时收到协调者的commit指令，它可以默认超时后自动提交，从而避免了在2PC中因协调者单点故障而导致的无限阻塞问题。",
    "source": "文档中「三阶段提交 (3PC)」部分",
    "hint": "3PC在2PC的基础上增加了一个阶段，这个阶段的名字直接体现了它的作用——在正式提交前的最后确认。"
  },
  {
    "question": "在TCC（Try-Confirm-Cancel）补偿型事务模型中，“Try”阶段的核心职责是什么？",
    "options": [
      "直接完成主要的业务操作",
      "检查业务可行性并预留资源",
      "撤销并回滚所有已执行的操作",
      "确认所有业务操作并释放资源"
    ],
    "correctAnswerIndex": 1,
    "explanation": "TCC模型的核心在于将业务逻辑拆分为三个部分。“Try”阶段并不执行最终的业务操作，而是进行业务检查（如检查库存、账户余额）并预留必要的业务资源（如冻结库存、冻结金额）。这一步是为后续的“Confirm”或“Cancel”做准备，确保第二阶段的操作能够成功执行。",
    "source": "文档中「TCC (Try-Confirm-Cancel) 补偿型事务」部分",
    "hint": "TCC的第一个字母代表了它的第一个阶段，这个阶段的主要目的是“尝试”执行，为后续的真正执行或取消做准备。"
  },
  {
    "question": "Saga模式是如何保证在长事务链中某个环节失败后，数据能达到最终一致性的？",
    "options": [
      "通过全局事务协调器锁定所有相关资源，失败时统一回滚。",
      "为每一个成功的正向操作，执行其对应的补偿操作进行“回滚”。",
      "无限次重试失败的环节，直到成功为止。",
      "将失败的事务请求放入死信队列，等待人工干预。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "Saga模式的核心思想是将一个长事务拆分为多个本地事务。每个本地事务都有一个对应的补偿操作。当长事务链中的某个本地事务失败时，Saga协调器会按相反的顺序调用所有已经成功执行的本地事务的补偿操作，从而撤销之前操作造成的影响，使系统数据恢复到事务开始前的状态，达到最终一致性。",
    "source": "文档中「Saga 模式」部分",
    "hint": "文档中描述Saga模式时提到：“如果Saga中的任何一个本地事务失败，系统会调用之前所有已成功执行的本地事务的补偿操作来撤销其影响。”"
  },
  {
    "question": "BASE理论是分布式系统设计的重要指导思想，其中“Soft state”（软状态）指的是什么？",
    "options": [
      "系统状态可以被轻易修改。",
      "系统允许在不同节点的数据副本之间存在中间状态，这个状态会随时间最终同步。",
      "系统的硬件状态不稳定，需要软件层面进行容错。",
      "系统状态只保存在内存中，不进行持久化。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "“Soft state”（软状态）与强一致性中的“状态必须时刻一致”相对。它允许系统中的数据副本在不同节点之间存在短暂的不一致，即存在一个数据同步的延迟。这个不一致的中间状态就是软状态，系统通过异步同步机制，保证数据最终会达到一致状态（Eventual Consistency）。",
    "source": "文档中「CAP 定律与 BASE 理论」部分",
    "hint": "BASE理论中的“软状态”和“最终一致性”是紧密相关的概念，它描述了数据从不一致到一致的过程中的一种状态。"
  },
  {
    "question": "Seata框架的AT模式能做到对业务的无侵入式支持，其实现自动回滚的关键是什么？",
    "options": [
      "它强制业务开发者为每个更新操作编写补偿方法。",
      "它在底层使用了高效的3PC协议来保证原子性。",
      "它通过解析SQL，在数据更新前后生成数据快照并记录到`undo_log`中。",
      "它在事务开始时对所有涉及的数据库表加上全局锁。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "Seata AT模式的精髓在于其“无侵入”特性。它通过代理数据源，在业务SQL执行前后，自动记录数据的“前镜像”和“后镜像”，并将这些信息存入`undo_log`表。当需要回滚时，Seata会根据`undo_log`中的记录自动生成反向的SQL语句来恢复数据，从而实现了对业务代码的零侵入，开发者无需手动编写补偿逻辑。",
    "source": "文档中「主流解决方案：Seata」的「AT 模式」部分",
    "hint": "AT模式的“A”代表“Automatic”，思考一下它是如何自动实现回滚的，而不需要开发者手动干预？"
  }
];
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                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  